Removal of Smoke and Acid Constituents from Flue Gases

Abstract

PRACTICAL remedies for preventing or reducing the emission of objectionable constituents in flue gases have in the past been mainly confined to the elimination of grit and dust emission. In large urban areas it is now realised that the acid emission is attended with more serious consequences. In 1927, Parliamentary sanction was only given to the erection of Battersea Power Station on the condition that the best practicable means should be taken to remove the oxides of sulphur from the flue gases. In a paper on a new method of removing smoke and acid constituents from flue gases read on January 7 to a joint meeting of the Institute of Fuel and the Institution of Electrical Engineers by Dr. J. L. Pearson, G. Nonhebel and P. H. N. Ulander, it was stated that the daily combustion of 1,000 tons of average coal in addition to grit, dust and tarry matter, leads to the formation of 45 tons of sulphuric acid, 3–7 tons of nitric acid and half a ton of hydrochloric acid. It is clear that when wet washing is applied, a non-effluent system must be used. The new system is a recirculating, non-effluent water system, from which the grit, dust and ashes are separated and removed as solids. A pilot plant was erected at Billingham, and was subjected to a twenty-months' running test. The water used was a hard surface water drawn from a local stream. Lime was used as the alkali for most of the test, and chalk was used for the remainder. Very satisfactory results were obtained. 97–99 per cent of the sulphur oxides were removed, 90–93 per cent of the hydrochloric acid and 97–98 per cent of the grit and dust from the pulverised fuel boiler. The exit gas from the plant is so free from sulphur dioxide that it is practically odourless, although the sense of smell can detect a very minute trace of this gas.